The invention is directed to a method for the angle-controlled turning of a part using a hydraulic piston/cylinder drive and a ratchet, and in particular to a method for operating a hydraulic power wrench.
WO 03/013797 A1 describes a method for controlling an intermittent screwing operation wherein a hydraulic power wrench with a piston/cylinder unit tightens a screw in several strokes. The screwing operation is divided into a torque mode effective until a predetermined assembly torque is reached, and a turning angle mode wherein, starting from the assembly torque, the screw is turned further through a predetermined angle. The power wrench is equipped with a torque sensor and a turning angle sensor. Such sensors represent an additional effort and implicate that only certain types of power wrenches can be used to implement this method.
A method from which the precharacterizing part of claim 1 starts is known from U.S. Pat. No. 5,668,328. Here, the angular variable of the hydraulic power wrench is used to determine the turning angle. The method assumes that the flow rate is constant and that the entire volume flow supplied is thus proportional to time. The turning angle of the power wrench is determined by a time measurement. Thereby, corresponding angle sensors may be dispensed with.
DE 198 13 900 A1 describes a method wherein the screw is tightened smoothly and without control until an assembly point is reached where the different parts of the screw connection are in snug fit. Thereafter, the screw tightening angle is measured, which is increased in several strokes, the durations of the individual strokes being accumulated. It is not detailed how reaching the assembly point is determined. It may be effected by detecting the transition from a smooth drive to a higher load and defining this as the assembly point.